使用JNI在C中访问Java对象中的Java对象

public class MyClass {
    public String myString = "Hello, world!";
}

javah -jni MyClass

#include <jni.h>
#include "MyClass.h"

JNIEXPORT jstring JNICALL Java_MyClass_getMyString(JNIEnv *env, jobject obj) {
    jfieldID myStringField = (*env)->GetFieldID(env, (*env)->GetObjectClass(env, obj), "myString", "Ljava/lang/String;");
    jstring myString = (jstring)(*env)->GetObjectField(env, obj, myStringField);
    return myString;
}

gcc -shared -o libmyclass.so -I${JAVA_HOME}/include -I${JAVA_HOME}/include/linux MyClass.c

System.loadLibrary("myclass");

MyClass myObj = new MyClass();
String myString = getMyString(myObj);